Method for imparting fire retardancy to organic resins

ABSTRACT

A free-flowing silicone polymer powder, having an average particle size of 1 to 1000 microns and prepared by mixing a polydiorganosiloxane with a silica filler, is uniformly dispersed in an organic resin using conventional equipment, such as a single screw or, preferably, a twin screw extruder. When employed at a concentration of about 0.5 to 25 parts by weight of powder per 100 parts by weight of resin, a significant improvement in the burn character of the modified resin is obtained such that the rate of heat release, generation of smoke and evolution of toxic carbon monoxide gas is significantly reduced relative to the unmodified resin.

FIELD OF THE INVENTION

The present invention relates to a method for imparting fire retardancyto an organic resin. More particularly, the invention relates to amethod for reducing the raze of combustion, evolution of carbon monoxideand formation of smoke when a thermoplastic or thermoset resin isburned, said method comprising modifying the resin with a certainsilicone polymer powder.

BACKGROUND OF THE INVENTION

Industrial utilization of plastics, particularly the so-calledengineering thermoplastics, has greatly increased over the past severaldecades. These materials have found their way into such diverseapplications as home and office furniture, airplane interiors, cabinetryand casing for electronic and computer systems and various componentsfor automobiles, machines and cookware, inter alia. Some of theseplastics, however, are not tough enough for the demanding applicationswhich continue to spring forth from the fertile minds of cost-consciousdesign engineers. In this regard, considerable effort has been devotedtoward the improvement of mechanical properties of the plastics, theenhancement of impact strength being particularly prized. To a limitedextent, these difficulties have been overcome by the addition of variousrubber compositions to thermoplastic resins.

For example, Liang et al., in U.S. Pat. No. 4,888,390, issued Dec. 19,1989, showed that certain rubbers could be used to improve the crackand/or impact resistance of a poly(phenylene sulfide) (PPS) resin. In asimilar approach, U.S. Pat. No. 3,920,770 to Nakashio et al., issued onNov. 18, 1975, teaches a poly(phenylene ether) (PPE) resin modified withvarious rubbery polymers. These compositions have improved elongationand impact resistance relative to unmodified resin.

Designers employing these plastic materials also place a high premium onfire retardancy since accidental fires continue to extract a heavy tollon life and property. Here, the thermoplastic and thermosetting resinsare less than satisfactory due to their organic (i.e., inherentlycombustible) nature. This deficit has also been addressed, most notablyby incorporating various halogen or phosphorous fire retardant compoundsin the plastic composition. A hydrated metallic compound, such as ahydrated alumina filler can also be used as fire retardant component,either by itself or in combination with the aforesaid compounds.Unfortunately, such tactics present disadvantages of their own: theaddition of hydrated fillers can detract from the mechanical propertiesof the modified plastic while many of the halogen and phosphorouscompounds are undesirable from a toxicological perspective.Additionally, even though the halogen compounds do impart flameresistance, their products of combustion are notoriously corrosive.Therefore, sensitive electronic components which have been exposed tothe fumes of burned plastics containing such compounds can sufferextensive corrosion damage even though they are otherwise unaffected bythe heat of the fire. The deleterious effects can occur months after theincidence of fire and the use of these compounds could foster a falsesense of security. There is therefore a need for modified plasticsystems which place less reliance on these conventional means ofachieving fire retardant properties. Some progress toward this end hasbeen made by modifying plastics with certain silicone components.

Thus, for example, a flame retardant PPE resin composition containing anaromatic alkenyl resin, a polyorganosiloxane graft copolymer, aphosphate and a particulate silicic acid is disclosed in U.S. Pat. No.5,064,887 to Yamamoto et al., issued on Nov. 12, 1991.

In U.S. Pat. No. 4,387,176, issued on Jun. 7, 1983 to Frye, athermoplastic flame retardant composition is disclosed which employs acombination of a silicone fluid or gum, a metal organic compound and asilicone resin as the modifier for the thermoplastic. A similar systemis shown by Frye et al. in U.S. Pat. No. 4,536,529, issued on Aug. 20,1985. In the latter patent, the modifying components include a siliconefluid, a metal soap precursor and a silicone resin. These compositionsare said to offer simpler processing and improved impact resistance overunmodified thermoplastics.

Smith et al., in U.S. Pat. No. 5,017,637, issued on May 21, 1991, teacha fire-retardant thermoplastic composition comprising an olefiniccopolymer or terpolymer, a polyorganosiloxane, a metal oxide hydrate anda dialdehyde. This composition finds utility in molding and extrusionapplications.

A flame retardant polymer composition which is essentially free ofhalogen compounds and organometallic salts is disclosed in EuropeanPatent Application 0393959 to BP Chemicals Ltd., published on Oct. 24,1990. This contribution to the art employs a combination of a siliconefluid or gum and an inorganic filler selected from compounds of a GroupIIA metal, to modify certain copolymers of ethylene. The filler istypically a compound such as magnesium oxide, magnesium carbonate orcalcium carbonate and the modified polymers are useful in wire and cableapplications.

In the elastomer art, it is also known to prepare organosiloxanecompositions in the form of a free-flowing powder prepared from a highconsistency "gum-type" polydiorganosiloxane and a reinforcing filler.There is, however, no suggestion to combine these with a thermoplasticresin as disclosed herein.

In accordance with the teaching of Link and Scarbel in U.S. Pat. No.3,824,208, issued Jul. 16, 1974, a powdered material is obtained byfirst reducing the particle size of the polydiorganosiloxane and thenmixing the particles with at least 15 parts by weight of a reinforcingfiller at a temperature of from 0° to 100° C. and under particular shearconditions.

Japanese Patent Publication No. 2/102007 to Toshiba Silicone Co.,published on Apr. 13, 1990, teaches pelletizing a high consistency or"gel" type vinyl-containing polydiorganosiloxane and then blending theresultant pellets with a filler. A processing aid is included to preventa phenomenon referred to as "creping" or "crepe hardening." Theresultant composition is then mixed using a high speed rotating blade at10° to 100° C. to produce a free-flowing powder.

Elastomers prepared from silicone rubber powders according to the abovecited teachings of Link and Scarbel and Japanese Patent Publication No.2/102007 were found to have a number of shortcomings, such as thepresence of undesirable gel particles which are discernable to theunaided eye as clear spots when the powdered rubber is combined with asuitable dye and massed into a thin section. This gel problem wasessentially overcome by the discoveries of Bilgrien et al., as disclosedin a copending application for patent entitled "Storage StableOrganosiloxane Composition and Method for Preparing Same," Ser. No.790,043, filed on Nov. 12, 1991, now U.S. Pat. No. 5,153,238, assignedto the assignee of the present invention and hereby incorporated byreference. The silicone rubber powder compositions of Bilgrien et al.have an average particle size of 1 to 1000 microns and are prepared byblending a high consistency polydiorganosiloxane into a quantity offluidized reinforcing filler that is heated to a temperature of >100° C.to 200° C. prior to, or immediately following, introduction of thepolydiorganosiloxane. The resultant rubber powders additionally exhibitexcellent storage stability and can be subsequently massed and cured toyield substantially gel-free elastomers having excellent physicalproperties.

The particular silicone rubber powder prepared according to thedisclosure of Bilgrien et al., cited supra, was found to be useful as amodifier for PPE resins and provided unexpected improvements in impactresistance and processability for only these polymers. This discoverywas disclosed by Romenesko et al. in copending application for patententitled "Poly(phenylene ether) Resin Modified with Silicone RubberPowder," Ser. No. 793,877, filed on Nov. 18, 1991 U.S. Pat. No.5,288,674, and assigned to the assignee of the present invention.

All of the above mentioned improvements in the modification of plasticresins notwithstanding, there is still a need for plastic materialshaving a greater degree of fire retardancy. Moreover, recent trends inthe art suggest that widely-accepted test methods used to evaluate thefire retardant character of plastics are not predictive of their reallife fire hazard. Conventional tests, such as Limited Oxygen Index(LOI), which is a measure of the minimum oxygen content of theatmosphere capable of sustaining combustion of the sample, andUnderwriters Laboratory method UL-94, wherein certain burn properties ofa vertical or horizontal test piece are determined (described in greaterdetail infra), only provide gross measures of flame resistance. Thelatter test is the industry's method of choice and various modifyingagents discussed above are typically added to plastics in order to passthis test.

However, neither of the above methods offers specific information aboutthe rate of heat generation in a fire; nor do these tests provideinformation about the rate of smoke generation or the production oftoxic gases as the samples are burned. It has been well documented thatthese are the predominant elements responsible for death and injury in areal fire situation. Thus, although the conventional tests may be wellestablished and easy to carry out, they are not good indicators of theactual liability associated with the burning of a given material sincethey do not measure the above mentioned elements of the combustionprocess.

A more promising evaluation of the critical parameters (rate ofcombustion and the evolution of smoke and carbon monoxide) has recentlybeen developed. This method, which has been codified as American Societyfor Testing and Materials standard ASTM E 1354-90, plays a key role inthe instant invention and is described in greater detail below. Itemploys a so-called cone calorimeter to obtain a quantitative display ofthe above mentioned combustion elements as a function of burn time.Using this method, the skilled artisan can quickly predict the relativecombustion hazard of a given new plastic formulation.

SUMMARY OF THE INVENTION

It has now been discovered that silicone rubber powders of the generaltype disclosed in above cited patent applications to Bilgrien et al. andRomenesko et al. can be used to modify resins other than poly(phenyleneether). When burned in a cone calorimeter, the thermoplastic orthermosetting resin compositions modified with this silicone rubberpowder unexpectedly exhibit significantly lower rates of heat generationand reduced smoke and carbon monoxide formation than the unmodifiedcontrols. Moreover, this improved flame retardant character can beachieved without resorting to the addition of the undesirable halogen,phosphorous or hydrate compounds. Additionally, the silicone rubberpowders are readily dispersible in the various resins using conventionalprocess equipment, such as a single screw or, preferably, a twin screwextruder. This offers a significant advantage to a plastics manufacturersince both resin and modifying rubber ingredients can be handled asfree-flowing solid feeds and are therefore amenable to facileintroduction to mixing equipment (e.g., from a hopper).

The present invention therefore relates to a method for imparting fireretardancy to an organic resin selected from the group consisting oforganic thermoplastic resins, said method comprising thoroughlydispersing a silicone polymer powder in said resin to form a modifiedresin composition, which, when burned, has a reduced rate of combustionand a reduced evolution of carbon monoxide and smoke relative to theunmodified resin, said silicone polymer powder having an averageparticle size of 1 to 1000 microns and consisting essentially of

(i) 100 parts by weight of a polydiorganosiloxane fluid or gum, and

(ii) from 10 to 150 parts by weight of a silica filler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents results of cone calorimeter tests on polystyrenesamples showing heat release as a function of burn time.

FIG. 2 represents results of cone calorimeter tests on the polystyrenesamples of FIG. 1 showing carbon monoxide evolution as a function ofburn time.

FIG. 3 represents results of cone calorimeter tests on the polystyrenesamples of FIG. 1 showing smoke evolution as a function of burn time.

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic or thermosetting resin (A) of the present invention iswell known in the art and may be a homopolymer or copolymer of any suchconventional system. Preferably, this component is a thermoplasticselected from polystyrene, high impact polystyrene, polypropylene,polycarbonate or poly(phenylene ether). Examples of other thermoplasticswhich may be modified according to the present invention arepolysulfones, poly(phenylene sulfide), acrylonitrile-butadiene-styrenecopolymers, nylons, acetal, polyethylene and copolymers thereof,poly(ethylene terephthalate), poly(butylene terephthalate), acrylics,fluoroplastics, thermoplastic polyesters, inter alia.

Examples of thermosetting resins which can be modified with the siliconepolymer powders of the invention include such systems as phenolics,epoxies, urethanes, unsaturated polyesters, polyimides, melamineformaldehyde and urea.

Component (B) of the present invention is a silicone polymer powderwhich consists essentially of 100 parts by weight of one or morepolydiorganosiloxanes (i) blended with about 10 to about 150 parts byweight of silica filler (ii).

The polydiorganosiloxane (i) used in the preparation of silicone polymerpowder (B) is a fluid or high consistency polymer or copolymer.Preferably, component (i)has the consistency of a gum and contains atleast one functional group selected from the group consisting ofhydroxyl and vinyl, in its molecule. The molecular weight of thispolymer is sufficient to impart a viscosity of from about 100 to about100,000,000 mPa-s (centipoise) to the polymer at 25° C. An alternatecharacterization of the viscosity of the polydiorganosiloxane gumsutilized in the present invention is the "Williams plasticity number,"as determined by the American Society for Testing and Materials (ASTM)test method 926. The plasticity number, as used herein, is defined asthe thickness in millimeters×100 of a cylindrical test specimen 2 cm³ involume and approximately 10 mm in height after the specimen has beensubjected to a compressive load of 49 Newtons for three minutes at 25°C. The high consistency polydiorganosiloxanes contemplated hereinpreferably have a Williams plasticity of about 150 to about 500.

The organic groups of the polydiorganosiloxane (i) are independentlyselected from hydrocarbon or halogenated hydrocarbon radicals such asalkyl and substituted alkyl radicals containing from 1 to 20 carbonatoms; alkenyl radicals, such as vinyl and 5-hexenyl; cycloalkylradicals, such as cyclohexyl; and aromatic hydrocarbon radicals, such asphenyl, benzyl and tolyl. Preferred organic groups are lower alkylradicals containing from 1 to 4 carbon atoms, phenyl, andhalogen-substituted alkyl such as 3,3,3-trifluoropropyl. Thus, thepolydiorganosiloxane can be a homopolymer, a copolymer or a terpolymercontaining such organic groups. Examples include gums comprisingdimethylsiloxy units and phenylmethylsiloxy units; dimethylsiloxy unitsand diphenylsiloxy units; and dimethylsiloxy units, diphenylsiloxy unitsand phenylmethylsiloxy units, among others. Most preferably, component(i) is a polydimethylsiloxane which is terminated with a vinyl group ateach end of its molecule and/or contains at least one vinyl group alongits main chain.

Methods for preparing fluid or high consistency (gum)polydiorganosiloxanes are sufficiently well known that they do notrequire a detailed discussion in this specification. For example, atypical method for preparing these polymers comprises the acid-orbase-catalyzed polymerization of cyclic diorganosiloxanes.

Component (ii) of the silicone polymer powder (B) is a finely dividedfiller derived from fume, precipitated or mined forms of silica. Theformer two fillers are typically characterized by surface areas greaterthan about 50 m² /gram. The fume form of silica is a preferredreinforcing filler based on its surface area, which can be as high as900 m² /gram, but preferably has a surface area of 50 to 400 m² /gram.When the less preferred mined silica (e.g., MINUSIL™) is employed, itshould be combined with at least an equal weight of a fume orprecipitated silica.

For the purpose of the present invention, the silica filler ispreferably treated by reaction with a liquid organosilicon compoundcontaining silanol groups or hydrolyzable precursors of silanol groups.Compounds that can be used as filler treating agents, also referred toas anti-creping agents, include such components as low molecular weightliquid hydroxy- or alkoxy-terminated polydiorganosiloxanes,hexaorganodisiloxanes and hexaorganodisilazanes. The silicon-bondedhydrocarbon radicals in all or a portion of the filler treating agentcan contain substituents such as carbon-carbon double bonds. It ispreferred that the treating compound is an oligomeric hydroxy-terminatedpolydimethylsiloxane having an average degree of polymerization (DP) of2 to about 100. A highly preferred treating fluid of this type has a DPof about 2 to about 10.

The silica filler used in the present method is preferably reacted withabout 10 to about 45 weight percent, based on filler weight, of thefiller treating agent prior to being blended with thepolydiorganosiloxane to form the silicone polymer powder (B). Treatmentof the filler can be carried out in the same mixing vessel used toprepare the silicone polymer powder. The silica or other reinforcingfiller is typically maintained at a temperature greater than 100° C. toabout 200° C. during the treatment process. Alternatively, the fillercan be treated while it is being blended with the high consistencypolydiorganosiloxane during preparation of the silicone polymer powder.In accordance with a preferred embodiment of the present method, thefiller treating agent is sprayed into the mixing chamber during blendingof the reinforcing filler with the polydiorganosiloxane, while thefiller and polydiorganosiloxane are in the highly turbulent, fluidizedstate characteristic of the present method.

In highly preferred embodiments of the present invention, analkoxysilane adhesion promoter (iii) is also incorporated in thesilicone polymer powder composition. This alkoxysilane adhesion promotercontains at least one alkoxy group having 1 to 4 carbon atoms and atleast one group selected from epoxy, acryloxy, methacryloxy, vinyl,phenyl or N-beta-(N-vinylbenzylamino)ethyl-gamma-aminoalkylhydrochloride in its molecule. Preferred alkoxysilane adhesion promotershave the general formula

    QSi(OMe).sub.3

wherein Me hereinafter denotes a methyl radical and Q is selected fromthe group consisting of an epoxyalkyl group, an acryloxyalkyl group, amethacryloxyalkyl group, a vinyl group, a phenyl group and anN-beta-(N-vinylbenzylamino)ethyl-gamma-aminoalkyl monohydrogen chloridegroup. Specific examples of such alkoxysilanes includegamma-acryloxypropyltrimethoxysilane,gamma-methacryloxypropyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane,N-beta-(N-vinylbenzylamino)ethyl-gamma-aminopropyltrimethoxysilanemonohydrogen chloride, phenyltrimethoxysilane and vinyltrimethoxysilane.

When the alkoxysilane adhesion promoter is employed, it is added at alevel of about 0.5 to about 15 parts by weight for each 100 parts byweight of said silicone polymer powder, the addition being preferablycarried out after the polydiorganosiloxane and treated silica fillerhave been mixed, as further described infra.

In addition to the above mentioned components, a number of additionalingredients can be added to the compositions of the present invention.These additional ingredients include but are not limited to extendingfillers such as quartz, calcium carbonate, and diatomaceous earth;pigments such as iron oxide and titanium oxide, electrically conductingfillers such as carbon black and finely divided metals, heat stabilizerssuch as hydrated cerric oxide, flame retardants such as halogenatedhydrocarbons, alumina trihydrate, magnesium hydroxide, organophosphorouscompounds and other fire retardant (FR) materials.

The silicone polymer powder (B) may be prepared in any mixing apparatuscapable of maintaining the reinforcing filler in a fluidized state whileblending the filler with the high consistency polydiorganosiloxane andapplying sufficient shear to reduce the size of the resultantfiller-coated polymer particles to a uniform powder having an averageparticle size of about 1 to about 1000 microns. Suitable mixers include,but are not limited to, Waring™ blenders having a high speed shearingblade at the bottom of a vertically oriented conical chamber and mixersmanufactured by Rheinstahl Henschel AG, Kassel, Germany.

Mixer/granulators manufactured by Littleford Bros. Inc. Florence, Ky.are preferred mixing devices. These mixers are referred to as "plow" or"plowshare" mixers due to the presence of at least one plow or"T"-shaped blade located in a horizontally oriented cylindrical mixingchamber. The plow blade rotates on the horizontal axis of the chamberwith the edge of the blade close to the perimeter of the chamber. Inaddition to maintaining the silica in a fluidized state and uniformlydispersing the polymer particles throughout the silica to achieve ahomogeneous blend, the plow blade is also believed to agglomerate theultimate particles produced by high speed shearing blade(s), alsopresent in the chamber, to achieve the desired final particle size. Thespeed of the plow blade required to maintain the silica in a fluidizedform is typically from 30 to about 200 revolutions per minute, and isd&pendent upon the capacity of the mixing chamber and the particle sizerange of the final powder. A speed of from 80 to 180 revolutions perminute is preferred using a 130 liter-capacity mixing chamber. The speedwould be proportionately slower for a larger capacity mixer. The mixingchamber also contains at least one high speed chopping blade to providethe shearing force required to reduce the particle size ofpolydiorganosiloxane to a fine powder. A preferred embodiment of amixing chamber contains at least one conical array of one to six bladesrotating on a single shaft and ranging in diameter from 4 to 9 inches(10 to 23 cm), the smallest diameter blade being located closest to themixer wall. It is believed that the speed of the chopping blade(s)should be between about 2000 to about 4000 revolutions per minute whenit is desired to prepare silicone polymer powders of the presentinvention with a processing time of up to 30 minutes.

In accordance with the preferred method for preparing the siliconepolymer powder (B), at least a portion of the reinforcing filler ismaintained in a highly turbulent, fluidized state in the mixingapparatus by stirring or otherwise agitating the filler particlessufficiently to break apart agglomerates, entrap air or other gasbetween the filler particles and maintain the particles suspended in themixing chamber. The suspended filler particles assume thecharacteristics of a fluidized bed with respect to the ability of thesuspended filler particles to rapidly coat the particles ofpolydiorganosiloxane that are added to the mixing apparatus togetherwith or shortly following addition of the filler. The additionalingredients described above can be added to the mixing chamber togetherwith the filler or with the polydiorganosiloxane. However, if thealkoxysilane adhesion promoter (iii) is to be used, this ingredientshould be added after the polydiorganosiloxane (i) and silica (ii) havealready been mixed.

In accordance with a preferred method, particles of treated silicafiller are fluidized and heated to a temperature of greater than 100° C.before the polydiorganosiloxane is added. To avoid or minimize thepresence of gel particles and reduce processing time, the temperaturewithin the mixing chamber is maintained at greater than 100° C. to about200° C., preferably greater than 100° C. to 150° C., during the entireprocess for preparing the silicone polymer powder (B), which typicallyrequires from 2 to 120 minutes, depending upon the amount of silica.

In a preferred embodiment of the present method and to reduce thecapacity of the mixing chamber required to prepare a given amount of thesilicone polymer powder, only a portion of the filler is addedinitially, due to the large increase in filler volume duringfluidization. This volume decreases substantially as the silicadensifies and coats the polydiorganosiloxane in the mixing chamber. Theremaining filler is initially placed in a hopper or other suitabledispensing container and allowed to drop into the chamber as the volumeof silica initially present in the mixer decreases due to densificationand coating of the polydiorgano-siloxane particles. This method offiller addition utilizes the full volume of the mixing chamberthroughout the process of preparing the finely divided organosiloxanecomposition.

The free-flowing silicone powder compositions prepared using the presentmethod can be stored for extended periods of time at temperatures up toabout 60° C. without undergoing any significant change in plasticity ofthe rubber.

A composition of the present invention may be prepared by thoroughlymixing from about 0.5 to about 25 parts by weight, preferably 1 to 15parts, of the silicone polymer powder (B) with 100 parts by weight ofresin (A). This mixing can be accomplished at elevated temperatures byany of the conventional methods used to disperse various components inhigh viscosity resins. The temperature and other conditions of such amixing operation is dependent upon the particular resin selected and maybe determined by routine experimentation by those skilled in the art.Alternatively, the silicone polymer powder can be premixed with resin(A) and the mixture then fed to an extruder. Examples of suitableequipment for this purpose include such machines as twin screw extrudersand single screw extruders, inter alia.

After components (B) and (A) are thoroughly mixed, the resultingmodified resin generally can be further processed by conventionaltechniques, such as extrusion, vacuum forming, injection molding, blowmolding or compression molding, to fabricate plastic parts. When burned,these parts have a reduced rate of heat release and generate less smokeand carbon monoxide than corresponding unmodified molding. Such partsfind utility in various industrial applications where a high degree offire retardancy is desired, particularly wherein the above mentionedelements of combustion pose a threat to human life and/or substantialloss of property. Examples of these applications include window and wallcoverings, electrical and electronic insulation components, such asmotor, coil and transformer insulation; housings for various electricaland electronic equipment, such as machines computers and hand tools;structural members furniture; automotive components, such as engine andinterior structural components; and aircraft interior components, interalia.

EXAMPLES

The following examples are presented to further illustrate the methodand compositions of this invention, but are not to be construed aslimiting the invention, which is delineated in the appended claims. Allparts and percentages in the examples are on a weight basis and allmeasurements were obtained at 25° C., unless indicated to the contrary.

Example 1

A silicone rubber powder of the present invention was prepared by firsttreating a silica filler and then blending the treated filler with apolydimethylsiloxane gum as follows.

The mixing chamber of a 130 liter capacity Littleford Mixer/Granulator(Model FM 130 D; Littleford Bros., Inc., Florence, Ky.) was heated andmaintained at a temperature of 135° C. Nitrogen was passed through themixer chamber at a flow rate of 3.40 m³ /sec (120 cubic feet per hour)(CFH). The nitrogen flow rate was then reduced to 0.283 m³ /sec (10 CFH)and about half of a 31.95 parts charge of a fume silica having a nominalsurface area of 250 m² /gram was added. The chopper and plow blades ofthe mixer were started (about 160 rpm for plow blade and about 3400 rpmfor chopper blades) and 6.80 part of a hydroxy-terminatedpolydimethylsiloxane fluid having a viscosity of about 0.00004 m² /sec(40 cS) and an average degree of polymerization (DP) of about 8 wassprayed into the mixer chamber using an atomizer nozzle. After about oneminute, 59.17 parts of a dimethylvinylsiloxy-terminatedpolydimethylsiloxane gum containing 0.142 mole percent ofmethylvinylsiloxane units and exhibiting a Williams plasticity number ofabout 150 was added to the mixer chamber. The remaining silica was thenintroduced in addition to 2.07 parts of an organosiloxane copolymerresin containing 7.2 mol percent of CH₃ SiO_(3/2) units, 24 mol percentof (CH₃)₂ SiO units, 3.2 mol percent of (CH₃)₃ SiO_(1/2) units, 15.4 molpercent of (CH₂ ═CH)(CH₃)SiO units and 50 mol percent of PhSiO_(3/2)units, wherein Ph hereinafter denotes a phenyl radical.

The nitrogen purge rate was increased to 3.40 m³ /sec (120 CFH) and thecontents were mixed for an additional 20 minutes, after which the mixerwas cooled to below 50° C. and a silicone rubber powder having theappearance of a free-flowing fine sugar powder was isolated.

Example 2

The procedure of Example 1 was followed with the exception that 1.75parts of an adhesion promoter, gammaglycidoxypropyltrimethoxysilane, wasadded after the 20 minute mixing step. This additional ingredient wasmixed at the elevated temperature for about 10 minutes before the abovedescribed cooling step was carried out. The resulting silicone rubberpowder was a free-flowing "crumbly" powder.

Modification of Polystyrene (PS)

Different silicone materials were used to modify a general purposepolystyrene resin (STYRON™ 685D; Dow Chemical Co.) at additive levels of5% and 15%. These blends were prepared in a Haake System 90 TW100extruder (Haake/Fisons Instruments, Paramus, N.J.) wherein the extruderzone 1 was set at 200° C. and zones 2 through 4 were set at 210° C.

Comparative compositions were also used to modify polystyrene resin andare defined as follows:

(Comparative) Example 1 was a trimethylsiloxy-terminatedpolydimethylsiloxane fluid having a viscosity of about 60 Pa-sec (60,000cP).

(Comparative) Example 2 was the dimethylvinylsiloxy-terminatedpolydimethylsiloxane gum containing 0.142 mole percent ofmethylvinylsiloxane units and exhibiting a Williams plasticity number ofabout 150 which was used in the preparation of Example 1.

(Comparative) Example 3 was a 2:1 blend of the polydimethylsiloxane gumof (Comparative) Example 2 and a mixture consisting essentially of 82percent of a dimethylvinylsiloxy end blocked polydimethylsiloxane havinga viscosity of about 3 Pa-sec (3,000 cP) and 18 percent of a benzenesoluble siloxane resin copolymer consisting essentially of (CH₃)₃SiO_(1/2) units and SiO₂ units in a molar ratio of approximately 0.75:1.

Each of the above blends, having the proportions shown in Table 1, wasmolded into test bars measuring 12.7×3.2×100 mm. The burn properties ofthese test bars were evaluated using a cone calorimeter according to themethod detailed in American Society for Testing and Materials standardASTM E 1354-90. In summary, eight of the above described test bars werearranged side-by-side on an aluminum foil tray so as to present a burnsurface of approximately 100 mm×100 mm and having a depth of 3.2 mm. Thetray containing the sample was placed on the platform of a load cell. Atruncated cone heater positioned above the sample was used to irradiatethe sample surface at a controlled heat flux of 30 kW/m². Testingcommenced with the removal of a heat shield to allow the incidentradiant energy to impinge upon the exposed surface of the sample. Aspark igniter placed between the cone heater and the sample was used toignite the gases generated as a result of heating. These gases, as wellas the smoke formed during the combustion, were drawn through the coneheater by an exhaust hood, the latter being connected to an exhaustblower through a duct. A gas probe in the duct sampled the combustiongases and was used to continuously monitor the formation of carbonmonoxide using an infrared analyzer. Similarly, a helium-neon lasersmoke meter within the duct was used to continuously measure the amountof smoke being formed as the sample burned, the smoke density reportedherein being a direct indication thereof. The heat released duringcombustion of the sample was calculated from a continuous determinationof the oxygen concentration in the exhaust stream and the flow ratethereof.

Representative results of cone calorimeter tests showing heat release,carbon monoxide production and smoke generation as a function of burntime of the polystyrene samples are plotted in FIGS. 1-3, respectively.The ordinate of FIG. 1 represents the heat released at a given time,measured in kW/m². The ordinate of FIG. 2 represents the amount ofcarbon monoxide released into the exhaust duct stream at a given time,measured in volts (i.e., % CO={volts-0.15}/5). The ordinate of FIG. 3represents the smoke density in the exhaust duct at a given time,measured in light extinction units. In each of these figures, curve 1represents the control material (i.e., unmodified PS resin); curve 3represents the PS resin modified with 15% of the polydimethylsiloxanegum of (Comparative) Example 2; and curve 2 represents the PS resinmodified with 5% of the silicone rubber powder of Example 1.Modification of the PS resin with 15% of the silicone rubber powder ofExample 1 did not result in a significant change relative to themodification with only 5% thereof and the former results were omittedfrom the figures for the sake of clarity.

The burn characteristics of the modified PS resins were compared withthe unmodified PS, as shown in Table 1. In each case, the value reportedis a calculated percentage of the respective property of the particularresin system relative to the peak value attained by the control resin,the former value being taken at the time that the control peak wasobserved. For example, the relative heat release of the PS resinmodified with the silicone rubber powder of Example 1 was calculated bydividing the peak heat release of this sample by the peak heat releaseof the control.

The relative values for peak heat, carbon monoxide (CO) formation andsmoke formation for the above described PS systems are presented inTable 1.

                  TABLE 1                                                         ______________________________________                                                         Burn Properties                                                               (Percent of Control)                                                            Peak   CO        Smoke                                     Composition        Heat   Formed    Formed                                    ______________________________________                                        Polystyrene        100    100       100                                       Control (0% silicone)                                                         Polystyrene Modified with:                                                    15% of (Comparative) Example 1                                                                   86     78        94                                        15% of (Comparative) Example 2                                                                   68     50        87                                        15% of (Comparative) Example 3                                                                   51     40        57                                        5% of Example 1    37     21        35                                        15% of Example 1   38     22        42                                        ______________________________________                                    

The results of Table 1 show that the silicone rubber powder of thepresent invention unexpectedly reduced the peak burn heat, carbonmonoxide production and smoke formation relative to unmodified PScompositions, as well as relative to PS modified with similar siliconegum or silicone gum/resin blends.

Modification of Poly(phenylene ether) (PPE)

Three different levels of the silicone rubber powder prepared in Example2 were blended with a poly(phenylene ether) resin using the abovedescribed TW100 extruder to form compositions of the present invention,the relative amounts of silicone and PPE being shown in Table 2. Theresin used, HPX-100L, was obtained from Mitsubishi Gas and Chemical,Tokyo, Japan and is described as a poly(2,6-dimethyl-1,4-phenyleneether). The extruder conditions employed were:

Feed zone 1 temperature=280° C.;

Mixing zone 2 temperature=310° C.;

Mixing zone 3 and exit zone 4 temperature=300° C.;

Screw speed=50 revolutions per minute (rpm);

Die=1/8 inch diameter strand die.

The extrudate from the above mixing operation was cooled, chopped intopellets, dried for 2.5 hours at 100° C. and fabricated into test barsmeasuring 12.7×3.2×100 mm using a Boy model 15S screw-type injectionmolding machine (Boy Machine Corp., Exton, Pa.). The molding parametersused were:

Mixing zone 1 and 2 temperatures=300° C.

Nozzle zone 3 dial setting=72.

Mold temperature=165° F.

Injection pressure=7,850 psi.

Screw discharge set point=2.0.

Mold clamp pressure=4,300 psi.

Screw speed=100 rpm.

Shot size dial=36.

Mold time=30 seconds.

The burn properties of these test bars were evaluated as described aboveusing the cone calorimeter according to ASTM E 1354-90. Results of thecone calorimeter tests are presented in Table 2, wherein a commercialPPE molding resin (NORYL™ 731) was used as a control, the flameproperties of the compositions of the present invention being ratedagainst this control. NORYL™ 731 is a product of the General ElectricCo., Pittsfield, Mass., and is believed to be a blend of about 30 to 40parts of high impact polystyrene (HIPS) in 70 to 60 parts ofpoly(2,6-dimethyl-1,4-phenylene ether) resin. This was used as a controlsince processing a 100% PPE sample could not be accomplished withoutdecomposing the polymer.

                  TABLE 2                                                         ______________________________________                                                     Burn Properties                                                               (Percent of Control)                                                            Peak     CO       Smoke                                        Composition    Heat     Formed   Formed                                       ______________________________________                                        NORYL ™ 731 100      100      100                                          Control (0% silicone)                                                         PPE Modified with:                                                            15% of Example 2                                                                             33       30       29                                           5% of Example 2                                                                              33       30       21                                           1% of Example 2                                                                              33       26       21                                           ______________________________________                                    

Modification of Polypropylene (PP)

The powder silicone rubber of Example 2 was used to modify apolypropylene resin (ESCORENE™ 5052; Exxon Chemical Polymers Group,Houston, Tex.) at the levels indicated in Table 3 using the abovedescribed blending method.

                  TABLE 3                                                         ______________________________________                                                        Burn Properties                                                               (Percent of Control)                                                            Peak    CO        Smoke                                     Composition       Heat    Formed    Formed                                    ______________________________________                                        Polypropylene     100     100       100                                       Control (0% silicone)                                                         Polypropylene Modified with:                                                  1% of Example 2   95.0    89.6      85.5                                      5% of Example 2   55.4    39.6      77.4                                      8% of Example 2   53.8    31.2      67.7                                      10% of Example 2  50.0    29.2      64.5                                      ______________________________________                                    

Modification of Polycarbonate (PC)

The powder silicone rubber of Example 2 was used to modify apolycarbonate resin (CALIBRE™ 0200-13; Dow Plastics, Midland, Mich.) atthe levels indicated in Table 4 using the above described blendingmethod.

                  TABLE 4                                                         ______________________________________                                                        Burn Properties                                                               (Percent of Control)                                                            Peak    CO        Smoke                                     Composition       Heat    Formed    Formed                                    ______________________________________                                        Polycarbonate     100     100       100                                       Control (0% silicone)                                                         Polycarbonate Modified with:                                                  1% of Example 2   55.2    40.9      38.5                                      5% of Example 2   41.4    23.3      44.4                                      ______________________________________                                    

From the above tables it can be seen that the resins modified with thesilicone rubber powder according to the present invention generatesignificantly less heat, carbon monoxide and smoke than thecorresponding unmodified resin when each is burned.

Modification of High Impact Polystyrene (HIPS)

To further illustrate the reduced burn resistance of the instantcompositions in combination with a conventional flame retardant, theformulations shown in Table 5 were prepared as described for the case ofthe PS samples. The resin used was STYRON™ 484-27-W high impactpolystyrene obtained from the Dow Chemical Co., Midland, Mich. This wastested as a control and also as modified with DECHLORANE™ PLUS 1000 andantimony oxide (Sb₂ O₃). DECHLORANE™ PLUS 1000 is a product of theOccidental Chemical Corporation (Grand Island, N.Y.) and is a highlychlorinated aromatic flame retardant additive.

Test bars measuring 3.2×12.7×127 mm (1/8×1/2×5 in) and 1.6×12.7×127 mm(1/16×1/2×5 inches), respectively, were prepared and subjected to flameresistance testing according to Underwriters Laboratory standard UL-94.In this procedure, the sample is held vertically and ignited with aBunsen burner (applied for 10 seconds), a cotton swab being placedbeneath the sample. The burn characteristics of the material is observedafter the burner is removed and these are grouped according to thefollowing classes:

    ______________________________________                                                       V-0    V-1       V-2                                           ______________________________________                                        Afterflame time for each                                                                       ≦10 sec                                                                         ≦30 s                                                                            ≦30 s                              individual specimen                                                           Total afterflame time for                                                                      ≦50 s                                                                           ≦250 s                                                                           ≦250 s                             any condition set of 5                                                        Afterflame plus afterglow time                                                                 ≦30 s                                                                           ≦60 s                                                                            ≦60 s                              for individual specimen after                                                 second flame application                                                      Cotton indicator ignited by                                                                    No       No        No                                        flaming particles or drops                                                    ______________________________________                                    

Results of burning the above HIPS and modified HIPS samples according toUL-94 is shown in Table 5. This table also shows cone calorimeterresults wherein the percentages indicated are relative to a controlbased on (Comparative) Example 4.

                  TABLE 5                                                         ______________________________________                                                                           (Com-                                                 Con- Example   Example  parative)                                             trol 4         5        Example 4                                  ______________________________________                                        Composition                                                                   HIPS         100    77        76     78                                       DECHLORANE ™                                                                            --     18        18     18                                       PLUS 1000                                                                     Sb.sub.2 O.sub.3                                                                           --      4         4      4                                       Example 2    --      1         2     --                                       UL-94 Results                                                                 3.2 mm bars  *      V-1       V-0    *                                        1.6 mm bars  *      V-2       V-2    V-2                                      Cone Calorimeter                                                              Results         Burn Properties (Percent of Control                           Peak Heat        66%      58       100                                        CO Formed        61%      57       100                                        Smoke Formed     55%      65       100                                        ______________________________________                                         * indicates that the sample burned completely in the vertical position an     could not be rated by this test.                                         

From Table 5 it can be seen that the compositions of the presentinvention, further comprising a conventional fire retardant combination,performed as well or better in the UL-94 test than a correspondingcomposition which did not contain the silicone rubber powder of Example2.

Example 6

A silicone polymer powder based on a polydimethylsiloxane fluid wasprepared having the composition:

(i) 3,876 parts silica having a surface area of 380 m² /g;

(ii) 4,260 parts dimethylvinylsiloxy end blocked polydimethylsiloxanehaving a viscosity of about 30 Pa-s;

(iii) 87 parts hydroxyl endblocked polydimethylsiloxane containing about10 weight percent vinyl radicals and about 16 weight percent hydroxylradicals;

(iv) 1,412 parts hexamethyldisilazane; and

(v) 180 parts water.

The powder was prepared in a manner similar to that described in Example1, as follows. A portion of the silica (1,934 parts) was introduced tothe mixer and pre-mixed for five minutes. Nitrogen was introduced at arate of 1.70 m³ /sec (60 CFH). Three hundred parts of thehexamethyldisilazane (iv) was then sprayed into the mixer and the systemheated for about 20 minutes using 483 kPa (70 psig) steam. The resultingtreated silica was discharged from the mixer and the process wasrepeated for the remaining silica to form a pre-treated silica.

Three thousand parts of the above described pre-treated silica was mixedin the Littleford equipment for five minutes and nitrogen was introducedat 1.70 m³ /sec. Polydimethylsiloxane (ii) was then added, followed bythe remaining silica. The water and component (iii) were added and thenthe remaining hexamethydisilazane was sprayed into the mixer. Mixing wascontinued for about 30 minutes while heating with 483 kPa steam toproduce a silicone polymer powder.

The above powder was used to modify the polystyrene resin, as describedabove, being added at a level of 5% thereto. Results of cone calorimetertests are presented in Table 6.

                  TABLE 6                                                         ______________________________________                                                     Burn Properties                                                               (Percent of Control)                                                            Peak     CO       Smoke                                        Composition    Heat     Formed   Formed                                       ______________________________________                                        Polystyrene    100      100      100                                          Control (0% silicone)                                                         Polystyrene Modified with:                                                    5% of Example 6                                                                               25       23       37                                          ______________________________________                                    

That which is claimed is:
 1. A modified resin composition consistingessentially of:(A) 100 parts by weight of an organic resin; and (B) from0.5 to 25 parts by weight of a silicone polymer powder, said siliconepolymer powder having an average particle size of 1 to 1000 microns andcomprising (i) 100 parts by weight of a polydiorganosiloxane polymer,and (ii) from 10 to 150 parts by weight of a filler selected from thegroup consisting of silica and treated silica, said powder optionallycontaining up to 15 parts by weight of an alkoxysilane adhesion promoterfor each 100 parts by weight of said silicone polymer powder,whereinsaid organic resin (A) is a polymeric system selected from the groupconsisting of polystyrene, high impact polystyrene, polypropylene,polycarbonate, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene-styrene copolymer, nylon, acetal, polyethylene,poly(ethylene terephthalate), poly(butylene terephthalate), acrylic,fluoroplastic, polyester, phenolic, epoxy, urethane, polyimide, melamineformaldehyde and urea.
 2. The composition according to claim 1, whereincomponent (ii) is a treated silica filler.
 3. The composition accordingto claim 2, wherein said polydiorganosiloxane (i) is apolydimethylsiloxane gum having at least one functional group selectedfrom the group consisting of hydroxyl and vinyl.
 4. The compositionaccording to claim 3, wherein said treated silica filler (ii) consistsessentially of a silica filler having a surface area of 50 to 400 squaremeters per gram treated with a hydroxy-terminated polydiorganosiloxanehaving a degree of polymerization of 2 to
 100. 5. The compositionaccording to claim 3, wherein said composition contains from 0.5 to 15parts by weight of an alkoxysilane adhesion promoter for each 100 partsby weight of said silicone polymer powder.
 6. The composition accordingto claim 5, wherein said treated silica filler (ii) consists essentiallyof a silica filler having a surface area of 50 to 400 square meters pergram treated with a hydroxy-terminated polydiorganosiloxane having anaverage degree of polymerization of 2 to
 100. 7. The compositionaccording to claim 6, wherein said alkoxysilane adhesion promoter isselected from the group consisting ofgamma-acryloxypropyltrimethoxysilane,gamma-methacryloxypropyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane,N-beta-(N-vinylbenzylamino)ethyl-gamma-aminopropyltrimethoxysilanemonohydrogen chloride, phenyltrimethoxysilane and vinyltrimethoxysilane.8. The composition according to claim 7, wherein said hydroxy-terminatedpolydiorganosiloxane has an average degree of polymerization of 2 to 10.9. A composition according to claim 1 wherein said silicone polymerpowder is prepared by mixing(i) 100 parts by weight of apolydiorganosiloxane polymer, and (ii) 10 to 150 parts by weight of afiller selected from the group consisting of silica and treated silica,said mixing being carried out in a temperature range of greater than100° C. to 200° C. and under sufficient shear to impart an averageparticle size of 1 to 1000 microns to said silicone polymer powder, saidfiller being maintained in a fluidized state during said mixing step,and said powder optionally containing up to 15 parts by weight of analkoxysilane adhesion promoter for each 100 parts by weight of saidsilicone polymer powder.
 10. The composition according to claim 1,wherein 1 to 15 parts by weight of said silicone polymer powder (B) iscombined with 100 parts by weight of said organic resin (A).
 11. Thecomposition according to claim 2, wherein 1 to 15 parts by weight ofsaid silicone polymer powder (B) is combined with 100 parts by weight ofsaid organic resin (A).
 12. The composition according to claim 3,wherein 1 to 15 parts by weight of said silicone polymer powder (B) iscombined with 100 parts by weight of said organic resin (A).
 13. Thecomposition according to claim 9, wherein component (ii) is a treatedsilica filler.
 14. The composition according to claim 13, wherein saidpolydiorganosiloxane (i) is a polydimethylsiloxane gum having at leastone functional group selected from the group consisting of hydroxyl andvinyl.
 15. The composition according to claim 14, wherein said treatedsilica filler (ii) consists essentially of a silica filler having asurface area of 50 to 400 square meters per gram treated with ahydroxy-terminated polydimethylsiloxane having a degree ofpolymerization of 2 to
 100. 16. The composition according to claim 14,wherein said composition contains from 0.5 to 15 parts by weight of analkoxysilane adhesion promoter for each 100 parts by weight of saidsilicone polymer powder (B).
 17. The composition according to claim 16,wherein said treated silica filler (ii) consists essentially of a silicafiller having a surface area of 50 to 400 square meters per gram treatedwith a hydroxy-terminated polydimethylsiloxane having an average degreeof polymerization of 2 to
 100. 18. The composition according to claim17, wherein said alkoxysilane adhesion promoter is selected from thegroup consisting of gamma-acryloxypropyltrimethoxysilane,gamma-methacryloxypropyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane,N-beta-(N-vinylbenzylamino)ethyl-gamma-aminopropyltrimethoxysilanemonohydrogen chloride, phenyltrimethoxysilane and vinyltrimethoxysilane.19. The composition according to claim 18, wherein saidhydroxy-terminated polydimethylsiloxane has an average degree ofpolymerization of 2 to
 10. 20. A method for imparting fire retardancy toan organic resin (A), said method comprising thoroughly dispersing insaid organic resin (A) a silicon polymer powder (B) to form a modifiedresin composition, said silicone polymer powder (B) having an averageparticle size of 1 to 1000 microns and consisting essentially of(i) 100parts by weight of a polydiorganosiloxane polymer, and (ii) from 10 to150 parts by weight of a filler selected from the group consisting ofsilica and treated silica, said powder optionally containing up to 15parts by weight of an alkoxysilane adhesion promoter for each 100 partsby weight of said silicone polymer powder,wherein said organic resin (A)is a polymeric system selected from the group consisting of polystyrene,high impact polystyrene, propylene, polycarbonate, polysulfone,poly(phenylene sulfide), acrylonitrile-butadiene-styrene copolymer,nylon, acetal, polyethylene, poly(ethylene terephthalate), poly(butyleneterephthalate), acrylic, fluoroplastic, polyester, phenolic, epoxy,urethane, polyimide, melamine formaldehyde and urea.
 21. The methodaccording to claim 20, wherein component (ii) is a treated silica fillerand wherein said modified resin composition, when burned, has a reducedrate of combustion and a reduced evolution of carbon monoxide and smokerelative to the unmodified resin.
 22. The method according to claim 21,wherein said polydiorganosiloxane (i) is a polydimethylsiloxane gumhaving at least one functional group selected from the group consistingof hydroxyl and vinyl.
 23. The method according to claim 22, whereinsaid treated silica filler (ii) consists essentially of a silica fillerhaving a surface area of 50 to 400 square meters per gram treated with ahydroxy-terminated polydiorganosiloxane having a degree ofpolymerization of 2 to
 100. 24. The method according to claim 22,wherein said silicone polymer powder contains from 0.5 to 15 parts byweight of an alkoxysilane adhesion promoter for each 100 parts by weightof said silicone polymer powder.
 25. The method according to claim 24,wherein said treated silica filler (ii) consists essentially of a silicafiller having a surface area of 50 to 400 square meters per gram treatedwith a hydroxy-terminated polydiorganosiloxane having an average degreeof polymerization of 2 to
 100. 26. The method according to claim 25,wherein said alkoxysilane adhesion promoter is selected from the groupconsisting of gamma-acryloxypropyltrimethoxysilane,gamma-methacryloxypropyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane,N-beta-(N-vinylbenzylamino)ethyl-gamma-aminopropyltrimethoxysilanemonohydrogen chloride, phenyltrimethoxysilane and vinyltrimethoxysilane.27. The method according to claim 26, wherein said hydroxy-terminatedpolydiorganosiloxane has an average degree of polymerization of 2 to 10.